Selenium

This is a general overview. For more in-depth information, see our health professional fact sheet.

What is selenium and what does it do?

Selenium is a nutrient that the body needs to stay healthy. Your thyroid gland needs selenium to produce hormones and function properly. Selenium is also needed for reproduction, to make DNA, to help protect cells, and to resist infection.

How much selenium do I need?

The amount of selenium that you need each day depends on your age. Average daily recommended amounts are listed below in micrograms (mcg).

What foods provide selenium?

Selenium is found naturally in many foods, especially foods that contain protein. You can get the recommended amounts of selenium by eating a variety of foods, including:

• Fish and other seafood
• Beef, pork, poultry, eggs, and dairy products
• Breads, cereals, and other grain products
• Beans, lentils, and nuts

What kinds of selenium dietary supplements are available?

Selenium is found in multivitamin/mineral supplements and other dietary supplements. It can be present in several different forms, including selenomethionine, selenium-enriched yeast, sodium selenite, and sodium selenate. All dietary supplements include a Supplement Facts label, which will tell you how much selenium is in that product.

Am I getting enough selenium?

Most people in the United States get enough selenium from the foods they eat. However, certain groups of people may have trouble getting enough selenium:

• People undergoing kidney dialysis
• People living with HIV
• People who eat diets that consist mostly of plant foods grown in local soils that are low in selenium. This is because the amount of selenium in soil can affect the selenium content of foods.

What happens if I don’t get enough selenium?

Selenium deficiency is very rare in the United States and Canada. Selenium deficiency can make iodine deficiency worse, increasing the risk of thyroid disease. Selenium deficiency can also cause Kashin-Beck disease (a type of arthritis that can begin in childhood) and Keshan disease (a type of heart disease that occurred mostly in the mid-20th century in China).

What are some effects of selenium on health?

Scientists are studying selenium to understand how it affects health. Here are some examples of what this research has shown.

Cancer

Getting enough selenium from your diet may lower your risk of some forms of cancer, including colorectal, prostate, lung, bladder, skin, esophageal, and gastric cancers.

Selenium supplements have been studied mostly in men to see if they reduce the risk of prostate cancer. These studies have found that selenium supplements do not lower the risk of prostate cancer, especially in men who get enough selenium from their diet.

More research is needed to understand the effects of selenium from food and dietary supplements on cancer risk.

Heart disease

Studies suggest that taking selenium supplements does not reduce the risk of heart disease, especially in people who get enough selenium from food. However, taking combination supplements that contain selenium and antioxidants, such as beta-carotene, vitamin C, or vitamin E, might lower the risk of dying of heart disease.

Cognitive decline and Alzheimer’s disease

Some research has shown that people with low selenium levels might have higher risks of cognitive decline and Alzheimer’s disease as they age, although most studies have not found that selenium supplements reduce these risks.

HIV infection

Children and adults with HIV who have selenium deficiency tend to have more severe disease. However, selenium supplements have shown little if any benefit for people with HIV.

While a few studies have found that pregnant women with HIV who take selenium supplements might have a lower risk of preterm birth, no other benefits have been found.

Male fertility

Selenium is an important nutrient for healthy sperm, and research shows that eating a healthy diet can improve sperm quality. However, it is unclear whether selenium supplements improve sperm quality.

More research is needed to determine whether selenium supplements affect male fertility.

Thyroid disease

Selenium is an important nutrient for the thyroid gland, and selenium levels are higher in the thyroid gland than in any other organ in the body. Research suggests that women who have low levels of selenium have a higher risk of thyroid disease, although a few studies have found that selenium supplements do not provide much benefit for the thyroid.

More research is needed to understand the effects of selenium on thyroid disease.

Can selenium be harmful?

Yes, if you get too much selenium over time. Brazil nuts, for example, contain very high amounts of selenium (68–91 mcg per nut) and can cause you to go over the upper limit if you eat too many. Getting excessive amounts of selenium from dietary supplements can also be harmful.

Getting too much selenium can cause:

• Garlic breath
• Metallic taste in the mouth
• Hair loss
• Brittle nails or nail loss
• Skin rash
• Nausea
• Diarrhea
• Extreme tiredness
• Irritability
• Nervous system problems

Consuming very high amounts of selenium can cause severe stomach and nervous system problems, difficulty breathing, tremors, lightheadedness, flushing, muscle tenderness, kidney or heart failure, and heart attacks. In rare cases, it can cause death.

The daily upper limits for selenium include intakes from all sources—food, beverages, and supplements—and are listed below. These upper limits do not apply if you are taking selenium under the care of a doctor.

Some experts recommend daily upper limits for selenium that are lower than these amounts. For example, in 2023 the European Food Safety Authority set a daily upper limit for selenium of 255 mcg for all adults, with lower amounts ranging from 70 to 230 mcg for children and teens, depending on age.

Does selenium interact with medications or other dietary supplements?

Yes, selenium may interact with certain medications, and some medications may interact with selenium. For example, cisplatin, a chemotherapy drug that is used to treat cancer, can lower selenium levels, but the effect this has on the body is not clear.

Tell your doctor, pharmacist, and other health care providers about any dietary supplements and prescription or over-the-counter medicines you take. They can tell you if the dietary supplements might interact with your medicines or if the medicines might interfere with how your body absorbs, uses, or breaks down nutrients.

Selenium and healthful eating

People should get most of their nutrients from food and beverages, according to the federal government’s Dietary Guidelines for Americans. Foods contain vitamins, minerals, dietary fiber, and other components that benefit health. In some cases, fortified foods and dietary supplements are useful when it is not possible to meet needs for one or more nutrients (for example, during specific life stages such as pregnancy). For more information about building a healthy dietary pattern, see the Dietary Guidelines for Americans and the U.S. Department of Agriculture’s (USDA’s) MyPlate.

Where can I find out more about selenium?

• For general information on selenium
  • Health Professional Fact Sheet on Selenium, Office of Dietary Supplements (ODS)
  • Selenium in Diet , MedlinePlus
• For more information on food sources of selenium
  • FoodData Central, USDA
  • Nutrient list for selenium (listed by food or by selenium content), USDA
• For more advice on choosing dietary supplements
  • Frequently Asked Questions: Which brand(s) of dietary supplements should I purchase?, ODS
• For information about building a healthy dietary pattern
  • Dietary Guidelines for Americans
  • MyPlate

Updated: June 18, 2025 History of changes to this fact sheet